build/gant.xml

<project name="Test gant invocation from Ant script" default="doGant">
  <dirname property="build.dir" file="${ant.file}"/>
  <property name="project.home" value="${build.dir}/.."/>
  <property name="gant.home" value="${project.home}/build/lib/gant"/>
  <property name="idea.lib" value="${project.home}/lib"/>
  <property name="gant.target" value="default"/>

  <path id="gant.classpath">
    <fileset dir="${gant.home}/lib">
      <include name="*.jar"/>
    </fileset>
    <fileset dir="${project.home}/build/lib/jps">
      <include name="*.jar"/>
    </fileset>
    <fileset dir="${idea.lib}">
       <include name="jdom.jar"/>
       <include name="log4j.jar"/>
       <include name="trove4j.jar"/>
       <include name="groovy-all-*.jar"/>
       <include name="protobuf*.jar"/>
       <include name="netty*.jar"/>
       <include name="asm4-all.jar"/>
       <include name="asm-commons.jar"/>
       <include name="jgoodies-forms.jar"/>
       <include name="guava*.jar"/>
       <include name="picocontainer.jar"/>
       <include name="jna.jar"/>
       <include name="jna-utils.jar"/>
       <include name="oromatcher.jar"/>
       <include name="cli-parser-*.jar"/>
       <include name="nanoxml-*.jar"/>
    </fileset>
  </path>

  <taskdef name="gant" classname="org.jetbrains.jps.gant.GantWithClasspathTask">
    <classpath refid="gant.classpath"/>
  </taskdef>

  <target name="doGant">
    <gant file="${gant.script}" target="${gant.target}"/>
  </target>
</project>